Field of the Invention
The present invention relates to a method of manufacturing a semiconductor device having a mesa stripe and to the semiconductor device.
Background Art
With the emergence of the problem of an abrupt increase in communication traffic and the installation space and power consumption problems with base stations attributable to the expansions of mobile broadband services and the further expansions of internet services such as moving image distribution services or social network services due to the rapid proliferation of smartphones, a need for preparation of high-speed, large-capacity and high-efficiency optical network infrastructures in trunk systems and access systems has arisen for communication of large-capacity data. There is a demand for further increasing the speed of operation of semiconductor laser elements serving as light sources in the optical network.
As one of factors in determining the upper limit of the frequency of modulation of a semiconductor laser element, a reduction in the efficiency of current injection into the active region due to a parasitic impedance is be mentioned. To reduce the parasitic impedance, the width of the process mesa is reduced. Japanese Patent Laid-Open No. 11-191654 discloses a semiconductor laser element having a narrow mesa structure.
Forming a mesa stripe of a reduced width requires etching a semiconductor layer with high accuracy. Trenches on opposite sides of a mesa stripe are ordinarily formed by dry etching. If the trenches are formed by dry etching with anisotropy, both the bottom and side surfaces of each trench are made flat, and stress is concentrated in portions where the flat bottom surface and the flat side surfaces meet each other (hereinafter referred to as “angular portion”). As a result of this stress concentration, splitting of the substrate not from the dicing street but from a point in the angular portions at the time of chip separation and hence a reduction in yield can occur.